1. Field of the Invention
This invention relates to bicycles, and especially to bicycle frames.
2. Prior Developments
Bicycles commonly have frames formed out of metal tubes welded together to form a relatively light frame construction designed to interconnect the front and rear wheels, while provided a support mechanism for the bicycle seat and handlebars.
A typical bicycle frame will comprise a relatively short upstanding front suspension tube adapted to receive the front fork structure for the front wheels, an elongated top support tube extending rearwardly from the front suspension tube, an elongated diagonal tube extending rearwardly and downwardly from the front suspension tube below the top support tube, and an elongated upstanding seat tube extending between the rear ends of the top tube and diagonal tube. A sprocket axle housing is located at the connection point between the diagonal tube and the upstanding seat tube.
The above-mentioned tubes are welded together so as to form a generally triangular frame structure, when viewed in side elevation.
The rear wheel of the bicycle has an axle that is supported in a bearing structure extending transversely between the connected ends of two rear fork structures located behind the above-mentioned triangular frame. One of the fork structures extends generally horizontally from the aforementioned sprocket axle housing. The other fork structure extends angularly downwardly from the upper end of the upstanding seat tube. The two rear fork structures cooperate with the elongated seat tube to form a second triangular frame. The elongated seat tube constitutes a common element of both triangular frames.
Bicycle frames are constructed so as to be as light as possible, while at the same time being relatively stiff and rigid. In some situations however, the bicycle frame is subject to premature failure, especially when the bicycle is used for acrobatic maneuvers that produce high impact forces between the terrain and the bicycle wheels. Shock forces can be alleviated to a certain extent by providing shock absorbers in the front wheel suspension. However, such shock absorbers do not absorb impact forces generated at the rear wheel.
The present invention is concerned with a bicycle frame that is relatively light, but is nevertheless relatively rigid and resistant to shock impact forces, especially forces generated by forcible impact of the bicycle rear wheel against the terrain surface. The construction, according to the invention, alleviates lateral as well as vertical flex of the frame, which may sometime pose a problem for the bicycle rider in the case of the conventional.